氮化鎵發光二極體光取出效率提升的研究

Abstract

本研究在探討如何利用高溫磷酸濕式化學蝕刻技術，來達到增加LED光萃取效率之目的。由於蝕刻結果取決於其晶格結構，蝕刻會沿者藍寶石的晶格面進行，這種方法主要是減少光在LED內部反射而造成的發光層及電子、電洞對光的吸收，光在內部反射的次數越多，路徑越長，則造成的損失越大。透過改變LED的幾何形狀，可以縮短光在LED內部的反射路徑，以期達到增加LED光萃取效率之目的。 研究方法首先製作切割道為30μm的Pattern，使用電漿輔助化學氣相沉積(Plasma Enhanced Chemical Vapor Deposition；PECVD)系統在藍寶石基板上方沉積SiO2，用Laser scribe先將切割道做切割動作，進而利用SiO2當作蝕刻遮罩層，在高溫磷酸與硫酸混合液中蝕刻藍寶石基板，進行藍寶石基板的側邊蝕刻(Side Wall Etching；SWE)，探討LED的光取出效率。研究方法分為三個：一是不同混合液濃度比例，在固定溫度及時間的條件。二是改變溫度條件下，固定混合液比例及時間的條件。三是改變時間，固定混合液比例及溫度的條件。將Wafer確認SWE Width (μm)及亮度的變化，並用SEM進行切割道及EPI Layer外觀分析，進行光電特性量測，發現本研究中提出的光取出效率方法，可以有效提高亮度。

In this thesis, we propose a method to increasing of LED light extraction by using high temperature wet etcher of phosphoric acid. In this method, we change geometric figure of LED chip. It decreased the reflection when the light met the sidewall of chip. The reflection occurred will increased possibility of light absorption. This technology was achieved by deposition SiO2 on sapphire using by plasma enhanced chemical vapor deposition (PECVD) and making the laser cut by laser scribe. The SiO2 was adopted the block layer and then etched in the mixture of high temperature phosphoric acid and sulfuric acid. The efficiency of sidewall etched profile on light extraction is shown in this thesis. There are three conditions of this study. The first was the changing concentrations of solution with fixed operation temperature and process time. Second was changing the operation temperature with fixed concentration of solution and process time. Third was changing the process time with fixed concentration of solution and process temperature. The results are verified by SWE width (μm), luminous intensity and SEM observation about laser scribe shape and epi layer sidewall profile. Base on the optical and the electrical characterization data, the method propsed in this thesis may increase the luminous intensity of LED through the light extraction efficiency.